1. Field of the Invention
The present invention relates to an adhesive dispenser and particularly to the art of controlling the amount of adhesive dispensed from the dispenser.
2. Related Art Statement
There is known an adhesive dispenser which iteratively dispenses a controlled amount of an adhesive from a reservoir therefor, by iteratively applying a pressure to the adhesive stored in the reservoir such that the controlled amount of adhesive is released from a nozzle connected to the reservoir via a supply passage and is applied to an object. In the known adhesive dispenser, the pressure applied to the adhesive is increased by supplying a pressurized gas to a space above the adhesive stored in the reservoir, and is decreased by communicating the space with the atmosphere. In the pressing state in which the pressure applied to the adhesive is increased, the adhesive is released from the nozzle and, in the gas-releasing state in which the air is released from the space above the adhesive to the atmosphere, the releasing of the adhesive is stopped. Accordingly, if the pressing state and the gas-releasing state are iteratively switched to each other in an appropriate manner, the adhesive can be applied in suitably controlled amounts to objects.
Since the viscosity of adhesive influences the amount of application of adhesive, the temperature of adhesive is maintained at an appropriate value, when the adhesive is applied. To this end, the whole dispenser is covered by a cover member, and the temperature of an entire inner space of the cover member is controlled by a cooler including a compressor, or a coil heater. That is, the temperature of adhesive is controlled by changing the temperature of the entire inner space of the cover member.
After the adhesive is applied to the object, the known dispenser is switched from the pressing state to the gas-releasing state. In the gas-releasing state, however, the pressure in the space above the adhesive cannot be quickly decreased down to values at which the releasing of adhesive stops. Thus, the releasing of adhesive cannot be quickly stopped. That is, the known dispenser cannot accurately control the amount of application of adhesive.
In addition, the known dispenser needs a long time for controlling the temperature of adhesive to a desired value, because the temperature of the inner space of the cover member must be controlled and additionally there is a time lag after the inner space is controlled to the desired value and before the temperature of adhesive in the reservoir is changed to the desired value. Moreover, much energy is needed for controlling the adhesive to the desired temperature. The cover member employed for covering the whole dispenser results in increasing the overall size of the dispenser.